hi dear

I am not a regular REGCMer, but can answer this one.  The model is
hydrostatic and therefore resolutions of 1km are not possible.  Usually
the limit for a hydrostatic model is about 7 to 8 km.  I understand some
people have used REGCM with 10km in the past.  Plans are afoot to create
a non-hydrostatic version of REGCM but this will take a while.

best,

Fattahi